VSB reception system with enhanced signal detection for processing supplemental data

ABSTRACT

A VSB reception system includes a sequence generator for decoding a symbol corresponding to the supplemental data and generating a predefined sequence included in the supplemental data at VSB transmission system. The reception system also includes a modified legacy VSB receiver for processing the data received from the VSB transmission system in a reverse order of the VSB transmission system by using the sequence, and a demultiplexer for demultiplexing the data from the modified legacy VSB receiver into the MPEG data and the supplemental data. The VSB reception system also includes a supplemental data processor for processing the supplemental data segment from the demultiplexer in a reverse order of the transmission system, to obtain the supplemental data, thereby carrying out the slicer prediction, decoding, and symbol decision more accurately by using the predefined sequence, to improve a performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/430,445, filed May 8, 2006, now U.S. Pat. No. 7,167,212 which is acontinuation of U.S. application Ser. No. 10/791,460, filed Mar. 1,2004, now U.S. Pat. No. 7,068,326, issued Jun. 27, 2006, which is acontinuation of U.S. application Ser. No. 09/933,206, filed Aug. 20,2001, now U.S. Pat. No. 6,760,077, issued Jul. 6, 2004, which pursuantto 35 U.S.C. § 119(a), claims the benefit of earlier filing date andright of priority to Korean Application No. 2001-3304, filed Jan. 19,2001, the contents of which are hereby incorporated by reference hereinin their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digital television reception system,and more particularly, to a 8T-VSB (Vestigial Sideband) reception systemresistant to ghost and noise and receiving and decoding supplementaldata in addition to MPEG data.

2. Description of the Related Art

The United States of America has employed ATSC 8T-VSB (8Trellis-Vestigial Sideband) as a standard since 1995, and has beenbroadcasting in the ATSC 8T-VSB since the later half of 1998. SouthKorea also has employed the ATSC 8T-VSB as a standard. South Koreastarted test broadcasting in May 1995, and has since August 2000 put inplace a regular test broadcasting system. The advancement of technologyallows the transmission of digital television (DTV) in the same 6 MHzbandwidth currently used by NTSC.

FIG. 1 illustrates a block diagram of a conventional ATSC 8T-VSBtransmission system 25 (“VSB transmission system”). The VSB transmissionsystem 25 generally comprises a data randomizer 1, Reed-Solomon coder 2,data interleaver 3, Trellis coder 4, multiplexer 5, pilot inserter 6,VSB modulator 7 and RF converter 8.

Referring to FIG. 1, there is a data randomizer 1 for receiving andmaking random MPEG data (video, audio and ancillary data). The datarandomizer 1 receives the MPEG-II data output from an MPEG-II encoder.Although not shown in FIG. 1, the MPEG-II encoder takes baseband digitalvideo and performs bit rate compression using the techniques of discretecosine transform, run length coding, and bi-directional motionprediction. The MPEG-II encoder then multiplexes this compressed datatogether with pre-coded audio and any ancillary data that will betransmitted. The result is a stream of compressed MPEG-II data packetswith a data frequency of only 19.39 Mbit/Sec. The MPEG-II encoderoutputs such data to the data randomizer in serial form. MPEG-II packetsare 188 bytes in length with the first byte in each packet always beingthe sync or header byte. The MPEG-II sync byte is then discarded. Thesync byte will ultimately be replaced by the ATSC segment sync in alater stage of processing.

In the VSB transmission system 25, the 8-VSB bit stream should have arandom, noise-like signal. The reason being that the transmitted signalfrequency response must have a flat noise-like spectrum in order to usethe allotted 6 MHz channel space with maximum efficiency. Random dataminimizes interference into analog NTSC. In the data randomizer 1, eachbyte value is changed according to known pattern of pseudo-random numbergeneration. This process is reversed in the VSB receiver in order torecover the proper data values.

The Reed-Solomon coder 2 of the VSB transmission system 25 is used forsubjecting the output data of the data randomizer 1 to Reed-Solomoncoding and adding a 20 byte parity code to the output data. Reed Solomonencoding is a type of forward error correction scheme applied to theincoming data stream. Forward error correction is used to correct biterrors that occur during transmission due to signal fades, noise, etc.Various types of techniques may be used as the forward error correctionprocess.

The Reed-Solomon coder 2 takes all 187 bytes of an incoming MPEG-II datapacket (the sync or header byte has been removed from 188 bytes) andmathematically manipulates them as a block to create a digital sketch ofthe block contents. This “sketch” occupies 20 additional bytes which areadded at the tail end of the original 187 byte packet. These 20 bytesare known as Reed-Solomon parity bytes. The 20 Reed-Solomon parity bytesfor every data packet add redundancy for forward error correction of upto 10 byte errors/packet. Since Reed-Solomon decoders correct byteerrors, and bytes can have anywhere from 1 to 8 errors within them, asignificant amount of error correction can be accomplished in the VSBreception system. The output of the Reed-Solomon coder 2 is 207 bytes(187 plus 20 parity bytes).

The VSB reception system will compare the received 187 byte block to the20 parity bytes in order to determine the validity of the recovereddata. If errors are detected, the receiver can use the parity bytes tolocate the exact location of the errors, modify the corrupted bytes, andreconstruct the original information.

The data interleaver 3 interleaves the output data of the Reed-Solomoncoder 2. In particular, the data interleaver 3 mixes the sequentialorder of the data packet and disperses or delays the MPEG-II packetthroughout time. The data interleaver 3 then reassembles new datapackets incorporating small sections from many different MPEG-II(pre-interleaved) packets. The reassembled packets are 207 bytes each.

The purpose of the data interleaver 3 is to prevent losing of one ormore packets due to noise or other harmful transmission environment. Byinterleaving data into many different packets, even if one packet iscompletely lost, the original packet may be substantially recovered frominformation contained in other packets.

The VSB transmission system 25 also has a trellis coder 4 for convertingthe output data of the data interleaver 3 from byte form into symbolform and for subjecting it to trellis coding. In the trellis coder 4,bytes from the data interleaver 3 are converted into symbols andprovided one by one to a plurality of Trellis coders and precoders 32-1and 32-12, shown in FIG. 7.

Trellis coding is another form of forward error correction. UnlikeReed-Solomon coding, which treated the entire MPEG-II packetsimultaneously as a block, trellis coding is an evolving code thattracks the progressing stream of bits as it develops through time.

The trellis coder 4 adds additional redundancy to the signal in the formof more (than four data levels, creating the multilevel (8) data symbolsfor transmission. For trellis coding, each 8-bit byte is split up into astream of four, 2-bit words. In the trellis coder 4, each 2-bit inputword is compared to the past history of previous 2-bit words. A 3-bitbinary code is mathematically generated to describe the transition fromthe previous 2-bit word to the current one. These 3-bit codes aresubstituted for the original 2-bit words and transmitted as the eightlevel symbols of 8-VSB. For every two bits that enter the trellis coder4, three bits come out.

The trellis decoder in the VSB receiver uses the received 3-bittransition codes to reconstruct the evolution of the data stream fromone 2-bit word to the next. In this way, the trellis coder follows a“trail” as the signal moves from one word to the next through time. Thepower of trellis coding lies in its ability to track a signal's historythrough time and discard potentially faulty information (errors) basedon a signal's past and future behavior.

A multiplexer 5 is used for multiplexing a symbol stream from thetrellis coder 4 and synchronizing signals. The segment and the fieldsynchronizing signals provide information to the VSB receiver toaccurately locate and demodulate the transmitted RF signal. The segmentand the field synchronizing signals are inserted after the randomizationand error coding stages so as not to destroy the fixed time andamplitude relationships that these signals must possess to be effective.The multiplexer 5 provides the output from the trellis coder 4 and thesegment and the field synchronizing signals in a time division manner.

An output packet of the data interleaver 3 comprises the 207 bytes of aninterleaved data packet. After trellis coding, the 207 byte segment isstretched out into a baseband stream of 828 eight level symbols. Thesegment synchronizing signal is a four symbol pulse that is added to thefront of each data segment and replaces the missing first byte (packetsync byte) of the original MPEG-II data packet. The segmentsynchronizing signal appears once every 832 symbols and always takes theform of a positive-negative-positive pulse swinging between the +5 and−5 signal levels.

The field synchronizing signal is an entire data segment that isrepeated once per field. The field synchronizing signal has a known datasymbol pattern of positive-negative pulses and is used by the receiverto eliminate signal ghosts caused by poor reception.

The VSB transmission system 25 also has the pilot inserter 6 forinserting pilot signals into the symbol stream from the multiplexer 5.Similar to the synchronizing signals described above, the pilot signalis inserted after the randomization and error coding stages so as not todestroy the fixed time and amplitude relationships that these signalsmust possess to be effective.

Before the data is modulated, a small DC shift is applied to the 8T-VSBbaseband signal. This causes a small residual carrier to appear at thezero frequency point of the resulting modulated spectrum. This is thepilot signal provided by the pilot inserter 6. This gives the RF PLLcircuits in the VSB receiver something to lock onto that is independentof the data being transmitted.

After the pilot signal has been inserted by the pilot inserter 6, theoutput is subjected to a VSB modulator 7. The VSB modulator 7 modulatesthe symbol stream from the pilot inserter 6 into an 8 VSB signal of anintermediate frequency band. The VSB modulator 7 provides a filtered(root-raised cosine) IF signal at a standard frequency (44 Mhz in theU.S.), with most of one sideband removed.

In particular, the eight level baseband signal is amplitude modulatedonto an intermediate frequency (IF) carrier. The modulation produces adouble sideband IF spectrum about the carrier frequency. The totalspectrum is too wide to be transmitted in the assigned 6 MHz channel.

The sidelobes produced by the modulation are simply scaled copies of thecenter spectrum, and the entire lower sideband is a mirror image of theupper sideband. Therefore using a filter, the VSB modulator discards theentire lower sideband and all of the sidelobes in the upper sideband.The remaining signal (upper half of the center spectrum) is furthereliminated in one-half by using the Nyquist filter. The Nyquist filteris based on the Nyquist Theory, which summarizes that only a ½ frequencybandwidth is required to transmit a digital signal at a given samplingrate.

Finally, there is a RF (Radio Frequency) converter 8 for converting thesignal of an intermediate frequency band from the VSB modulator 7 into asignal of a RF band signal, and for transmitting the signal to areception system through an antenna 9.

The foregoing VSB communication system is at least partially describedin U.S. Pat. Nos. 5,636,251, 5,629,958 and 5,600,677 by Zenith Co. whichare incorporated herein by reference. The 8T-VSB transmission system,which is employed as the standard digital TV broadcasting in NorthAmerican and South Korea, was developed for the transmission of MPEGvideo and audio data. As technologies for processing digital signalsdevelop and the use of the Internet increases, the trend currently is tointegrate digitized home appliances, the personal computer, and theInternet into one comprehensive system.

FIG. 2 illustrates a related art ATSC 8T-VSB reception system 150 (“VSBreception system”). In FIG. 2, there is a demodulator 11 for receiving aRF band signal through an antenna 10 and converting the RF band signalinto a base band signal, a synchronizing and timing recovery (not shown)for recovering a segment synchronizing signal, a field synchronizingsignal and symbol timing.

There is a comb filter 12 for removing an NTSC interference signal, anda channel equalizer 13 for correction of a distorted channel by using aslicer predictor 14. A phase tracker 15 is provided for correcting aphase of a received signal, and a Trellis decoder 16 for subjecting thephase corrected signal to Viterbi decoding. There is a datadeinterleaver 17 for carrying out a reverse action of the datainterleaver 3 in the transmission system, and a Reed-Solomon decoder 18for decoding the Reed-Solomon coded signal.

The VSB reception system 150 further includes a data derandomizer 19 formaking a reverse action of the data randomizer 1 in the transmissionsystem. Thus, the VSB reception system 150 can receive only the MPEGdata, and no supplemental data. Accordingly, the development of areception system that can receive the supplemental data as well as theMPEG video and audio data is needed. Moreover, the predictionreliability of the slicer predictor 14 in the VSB reception system 150,which predicts a signal level group, degrades the presence of excessivechannel noise or an excessive ghost.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a VSB reception systemthat substantially obviates one or more of the problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a digital VSB receptionsystem which can receive both MPEG data and supplemental data.

Another object of the present invention is to provide a digital VSBreception system which has significantly improved performance overchannel noise and ghost than the related art ATSC 8T-VSB receptionsystem.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a VSBreception system for receiving and decoding an input signal (comprisingan MPEG data segment and a supplemental data segment) transmitted from aVSB transmission system comprises a sequence generator for indicating asymbol corresponding to the supplemental data and generating apredefined sequence encoded with the supplemental data; a modifiedlegacy VSB receiver for processing the input signal received from theVSB transmission system in a reverse order of the VSB transmissionsystem and outputting a derandomized data signal; a demultiplexer fordemultiplexing the derandomized data signal from the modified legacy VSBreceiver into the MPEG data segment and an encoded supplemental datasegment; and a supplemental data processor for decoding the encodedsupplemental data segment from the demultiplexer to obtain thesupplemental data segment.

According to one aspect of the present invention, the sequence generatorincludes a multiplexer for receiving and multiplexing a supplementaldata dummy packet and an MPEG data dummy packet; a randomizer forrandomizing an output signal of the multiplexer; a parity inserter forinserting dummy bytes to randomized data; a data interleaver forinterleaving an output of the parity inserter; and a trellis coder forconverting interleaved data to symbols and outputting the convertedsymbols without subjecting to trellis coding. Preferably, the trelliscoder includes a plurality of coders and precoders for receiving thesymbols and forwarding the symbols without subjecting to precoding andcoding. The randomizer subjects the output signal of the multiplexerusing pseudo random bytes and 0x55 to a bit-wise AND logical operation,and a result of the AND logical operation and input bits from themultiplexer to a bit-wise exclusive OR logical operation.

According to another aspect of the present invention, the symbols fromthe trellis coder includes two bits D1 and D0, wherein if the bit D1 isat a first logic level, a symbol corresponds to a supplemental datasymbol, and if the bit D1 is at a second logic level, the symbol is anMPEG data symbol, and when the bit D1 is at the first logic level, thebit D0 is the predefined sequence being used to decode the supplementaldata segment.

According to another aspect of the present invention, the dummy bytescorrespond to the 20 parity bytes are dummy byes of 0x00, and the MPEGdata dummy packet produces 187 dummy bytes of 0x00, and the supplementaldata dummy packet produces three dummy bytes of 0x00 corresponding tothe MPEG header bytes, and 184 dummy bytes of 0xAA corresponding to thesupplemental data packet.

According to another aspect of the present invention, the modifiedlegacy VSB receiver includes a demodulator for receiving the inputsignal through and converting the input signal into a base band signal,and recovering a segment synchronizing signal, a field synchronizingsignal, and a symbol timing from the base band signal; a comb filter forremoving an NTSC interference signal from an output signal of thedemodulator, if the NTSC interference signal is detected; a slicerpredictor for providing a slicer prediction signal and a predictionreliability signal by using a predefined sequence from the sequencegenerator; a channel equalizer for correcting a distorted channel in anoutput signal of the comb filter by using the slicer prediction signalthe prediction reliability signal and the predefined sequence andoutputting a channel equalizer output signal; a phase tracker forcorrecting a phase of an output signal of the channel equalizer by usingthe predetermined sequence and the slicer prediction signal from atrellis decoder; a trellis decoder for decoding an output of the phasetracker using Viterbi algorithm and the predefined sequence receivedfrom the sequence generator; a data deinterleaver for deinterleaving atrellis decoder output signal; a Reed-Solomon decoder for decoding aReed-Solomon coded signal outputted from the data deinterleaver; and adata derandomizer for derandomizing a Reed-Solomon decoder outputsignal.

According to another aspect of the present invention, the supplementaldata processor includes an MPEG header remover for removing three MPEGheader bytes from the supplemental data segment received from thedemultiplexer; a null sequence remover for removing the null sequenceinserted to the supplemental data packet; and a Reed-Solomon decoder forsubjecting a null sequence remover output to Reed-Solomon decoding.There may be provided, a deinterleaver between the null sequence removerand the Reed-Solomon decoder for deinterleaving the null sequenceremover output.

According to another aspect of the present invention, the channelequalizer includes a plurality of slicers each having a predeterminedsignal level detector; a feed-forward filter for receiving a comb filteroutput signal; a feedback filter for receiving an output signal of oneof the plurality of slicers; an adder for adding output signals of thefeed-forward filter and the feedback filter and outputting an addedsignal as a channel equalizer output signal, wherein the plurality ofslicers commonly receive the added signal; a multiplexer for outputtingone of the outputs of the plurality of slicers to the feedback filter inresponse to a control signal; and a controller for updating filtercoefficients of the feed-forward filter and the feedback filter andproviding the control signal to the multiplexer in response to amultiplexer output signal, the slicer prediction signal, and theprediction reliability signal, the channel equalizer output signal andthe predefined sequence to select the multiplexer to output signal fromone of the plurality of slicers that has the predetermined signal leveldetector closes to the comb filter output signal.

According to another aspect of the present invention, the slicerpredictor receives the channel equalizer output signal, the predefinedsequence generated from the sequence generator and information that thesymbol received is of the supplemental data packet, estimates a registervalue of the trellis coder, calculates prediction reliability, andforwards the estimated register value and the prediction reliabilitysignal to the controller of the channel equalizer.

According to another aspect of the present invention, the plurality ofslicers includes first to third slicers for processing MPEG datasymbols, and fourth to ninth slicers for processing the supplementaldata symbols. The first slicer has 8 level values −7, −5, −3, −1, +1,+3, +5, +7, the second slicer has 4 level values of −7, −3, +1, +5, thethird slicer has 4 level values of −5, −1, +3 +7, the fourth slicer has4 level values of −7, −5, +1, +3, the fifth slicer has 4 level values of−3 −1, +5, +7, the sixth slicer has 2 level values of −7, +1, theseventh slicer has 2 level values of −5, +3, the eighth slicer has 2level values of −3, +5, and the ninth slicer has 2 level values of −1,+7. Preferably, −7 denotes 000, −5 denotes 001, −3 denotes 010, −1denotes 011, +1 denotes 100, +3 denotes 101, +5 denotes 110, and +7denotes 111.

According to another aspect of the present invention, with respect tothe MPEG data symbols, the first slicer is selected in a low reliabilitycase, the second slicer is selected for a high reliability case and theestimated register value is at a first logic level, and the third sliceris selected for a high reliability case and estimated register value isat a second logic level.

According to another aspect of the present invention, with respect tothe supplemental data symbols one of the fourth slicer and the fifthslicer is selected in response to the predefined sequence for a lowreliability case; the sixth slicer is selected for a high reliabilitycase and the predefined sequence value and the estimated register valueare at a first logic level; the seventh slicer is selected for a highreliability case and the predefined sequence value is at a first logiclevel and the estimated register value is at a second logic level; theeighth slicer is selected for a high reliability case and the predefinedsequence value is at a second logic level and the estimated registervalue is at a first logic level; and the ninth slicer is selected for ahigh reliability case and the predefined sequence value and theestimated register value are at a second logic level.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description, serve to explain the principles of theinvention.

FIG. 1 illustrates a block diagram showing an ATSC 8T-VSB transmissionsystem;

FIG. 2 illustrates a block diagram showing an ATSC 8T-VSB receptionsystem;

FIG. 3 illustrates a block diagram of a VSB transmission system fordigital TV broadcasting in accordance with a preferred embodiment of thepresent invention;

FIG. 4 illustrates a diagram for explaining insertion of a nullsequence;

FIG. 5 illustrates a block diagram of a Trellis coder and a precoder;

FIG. 6 illustrates a state transition diagram of an ATSC 8T-VSB Trelliscoder;

FIG. 7 illustrates a functional diagram of an ATSC 8T-VSB Trellis coder;

FIG. 8 illustrates a block diagram of a VSB reception system inaccordance with a preferred embodiment of the present invention;

FIG. 9 illustrates a block diagram of a sequence generator in accordancewith a preferred embodiment of the present invention;

FIG. 10A illustrates signal level diagrams of slicers used for MPEG datasymbols;

FIG. 10B illustrates signal level diagrams of slicers used forsupplemental data symbols; and

FIG. 11 illustrates a block diagram of a channel equalizer in accordancewith a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 3 illustrates a block diagram showing a VSB transmitter 95 for thetransmission of the supplemental and MPEG data in accordance with apreferred embodiment of the present invention. In FIG. 3, the VSBtransmitter 95 includes a VSB supplemental data processor 90 and a VSBtransmission system 25. The description of the VSB transmission system25 is described above in connection with FIG. 1, and thus, will not berepeated. According to the preferred embodiment of the presentinvention, the VSB supplemental data processor 90 includes aReed-Solomon coder 20, a data interleaver 21, a null sequence inserter22, an MPEG header inserter 23, a multiplexer 24, an 8T-VSB transmissionsystem 25, and an antenna 26.

As shown in FIG. 3, for the transmission of the supplemental data fromthe VSB transmitter 95 (i.e., a broadcasting station) to a VSB receptionsystem on a channel (terrestrial or cable), the VSB transmitter 95subjects the supplemental data to various digital signal processes. Toprovide backward compatibility of the present invention with existingdevices, the supplemental data is preferably 164 byte packet which willeventually be processed to be a 187 byte packet before entering the VSBtransmission system 25. However, the size of the supplemental datapacket may be varied so long as the output of the VSB supplemental dataprocessor 90 is compatible with the VSB transmission system 25.

In the VSB supplemental data processor 90, there is provided aReed-Solomon coder 20 for the correction of errors. The supplementaldata is coded at a Reed-Solomon coder (or R-S coder) 20. Preferably, theReed-Solomon coder 20 is used for subjecting the supplemental data toReed-Solomon coding and adding a 20 byte parity code to the output data.As described above, Reed-Solomon encoding is a type of forward errorcorrection scheme applied to the incoming data stream. Forward errorcorrection is used to correct bit errors that occur during transmissiondue to signal fades, noise, etc. Various other types of error correctiontechniques known to one of ordinary skill in the art may be used as theforward error correction process.

According to the preferred embodiment, the Reed-Solomon coder 20 of theVSB supplemental data processor takes 164 bytes of an incomingsupplemental data packet and mathematically manipulates them as a blockto create a digital sketch of the block contents. The 20 additionalbytes are added at the tail end of the original 164-byte packet. These20 bytes are known as Reed-Solomon parity bytes. Since Reed-Solomondecoders of the VSB reception system correct byte errors, and bytes canhave anywhere from 1 to 8 bit errors within them, a significant amountof error correction can be accomplished in the VSB reception system. Theoutput of Reed-Solomon coder 20 is preferably 184 bytes (164 bytes fromthe original packet plus 20 parity bytes).

The VSB supplemental data processor 90 further includes the datainterleaver 21, which interleaves the output data of the Reed-Solomoncoder 20. The data interleaver 21 is for interleaving the codedsupplemental data to enhance performance against burst noise. The datainterleaver 21 may be omitted, if it is not required to enhance theburst noise performance of supplements data.

The data interleaver 21 according to the preferred embodiment mixes thesequential order of the supplemental data packet and disperses or delaysthe supplemental data packet throughout time. The data interleaver 21then reassembles new data packets incorporating small sections from manydifferent supplemental data packets. Each one of the reassembled packetsare preferably 184 bytes long.

As described above, the purpose of the data interleaver 21 is to preventlosing of one or more packets due to noise or other harmful transmissionenvironment. By interleaving data into many different packets, even ifone packet is completely lost, the original packet may be recovered frominformation contained in other packets. However, because there is a datainterleaver in the ATSC 8T-VSB transmission system, the data interleaverfor the supplemental data can be omitted if it is not required toenhance the burst noise performance of the supplemental data. For thisreason, the data interleaver 21 may not be necessary for the VSBsupplemental data processor 90.

The VSB supplemental data processor 90 also includes the null sequenceinserter 22 for inserting a null sequence to an allocated region of theinterleaved (if the data interleaver 21 was present) or Reed-Solomoncoded supplemental data for generating the predefined sequence for thesupplemental data at an input terminal of a Trellis coder (shown in FIG.1). The null sequence is inserted so that the VSB reception systemreceives the supplemental data reliably, even in a noisy channel ormultipath fading channel. An example structure of the transmission dataformed by the insertion of the null sequence will be explained below indetail with reference to FIG. 4.

Further referring to FIG. 3, THE VSB supplemental data processor 90includes the MPEG header inserter 23 for adding an MPEG header to thesupplemental data having the null sequence inserted thereto, forbackward-compatibility with the legacy VSB reception system. Because theMPEG-II data supplied to the VSB transmission system 25 is 187 byteslong, the MPEG header inserter 23 places, preferably, three headers infront of each packet (which was 184 bytes) to form a 187 byte longpacket identified to the MPEG-II data packet.

The supplemental data have the MPEG header added thereto is provided toa multiplexer 24. The multiplexer 24 receives as inputs the processedsupplemental data from the MPEG header inserter 23 and MPEG datapackets. MPEG data packet, such as a broadcasting program (movie,sports, entertainment, or drama), coded through a different signal path(output from MPEG encoder), is received together with the supplementaldata at the multiplexer 24. Upon reception of the MPEG data and thesupplemental data, the multiplexer 24 multiplexes the supplemental dataand the MPEG data at a fixed ratio under the control of a controllerdefining a multiplexing ratio and unit and forwards the multiplexed datato the 8T-VSB transmission system 25.

The VSB transmission system 25, which is described in detail inreference to FIG. 1, processes the multiplexed data and transmits theprocessed data to the VSB reception system through the antenna 26.

For example, the Reed-Solomon coder 20 uses a code having a block sizeN=184, a payload K=164, and an error correction capability T=10. On theother hand, as a generator polynomial of the Galois Field and theReed-Solomon coder 20, the same code as the Reed-Solomon coder 2described with respect to FIG. 1 may be used. According to the preferredembodiment, other values of the block size N, the payload K, and theerror correction capability T may be used in the Reed-Solomon coder 20in FIG. 3. For an example, a code having N=184, K=154, and T=15 may beused, or a code having N=92, K=82, and T=5 may be used. Although theReed-Solomon code is used in the present invention, other code suitablefor error correction known to one of ordinary skill in the art may beused therein.

In the VSB transmission system 25, one data field has 313 segments: 312data segments 124 and one field synchronizing segment 122. The 312 datasegments have data segments of the supplemental data and the MPEG datasegments. Each data segment has 184 byte data, a 3 byte MPEG header, andthe 20 byte Reed-Solomon parity. The 3 byte MPEG header will be used bythe MPEG decoder in the VSB reception system.

The use of the MPEG header is explained in more detail. ISO/IEC 13818-1has a definition on an MPEG transport packet header. If a 0x47synchronization byte is removed from the MPEG transport packet header, a3 byte header is left. A PID (program identification) is defined by this3 bytes. A transport part of the MPEG decoder discards a packet if thePID of the received packet received is not valid. For example, a nullpacket PID or other reserved PID can be used. Therefore, the MPEG headerinserter 14 in FIG. 2 inserts the 3 byte header containing such a PIDinto the supplemental data packet. Therefore, the supplemental data canbe discarded at the MPEG decoder of the legacy VSB receiver.

The VSB reception system determines the multiplexing locations of theMPEG data and the supplemental data in the field data receivedsynchronous to the field synchronizing signal. The VSB reception systemdemultiplexes the MPEG data and the supplemental data based on themultiplexing locations. A multiplexing ratio and method for multiplexingthe MPEG data and the supplemental data may vary with amounts of datathereof.

Information on the variable multiplexing method and ratio may be loaded,for example, on a reserved area of the 92 bits not used in the fieldsynchronizing signal. By retrieving and decoding such information, theVSB reception system identifies the correct multiplexing ratio andmethod from the multiplexing information contained in the fieldsynchronizing signal.

Alternatively, the multiplexing information may be inserted, not only inthe reserved area of the field synchronizing signal, but also in thedata segment of the supplemental data. One of the supplement datasegment may be used to transmit the multiplexing information for use bythe VSB reception system.

FIG. 4 illustrates a diagram for explaining the process for inserting anull sequence into the supplemental data at the null sequence inserter22 in FIG. 3 to generate the predefined sequence at the input of thetrellis coder.

The VSB transmission system inserts the predefined sequence into thesupplemental data before transmission for performance enhancement of theVSB reception system. The sequence has a series of ‘1’s and ‘0’sarranged in an order fixed in advance. The numbers of ‘1’ and ‘0’ arerequired to be the same in average. For example, the predefined sequencemay be an output of a pseudo random sequence generator whose initialvalue is fixed in advance. As shown in FIG. 4, upon reception of one bitof supplemental data, the null sequence inserter 22 inserts one null bittherein, to provide 2 bits. The null bit is randomized in the 8T-VSBtransmission system in FIG. 3, and then subjected to Reed-Solomoncoding. The coded supplemental data is interleaved, and applied to aTrellis coder (not shown) as an input d0. The input signal d0 is a loworder bit of the two bits applied to the Trellis coder.

FIG. 4 illustrates an example of inserting the null sequence into thesupplemental data by the null sequence inserter 22 according to thepreferred embodiment of the present invention. The supplemental datahaving the null sequence inserted therein is transmitted to the VSBreception system. The predefined sequence has 1's and 0's arranged in afixed order. The predefined sequence inserted in the supplemental datacan be used for performance improvement in the reception system.

For example, the channel equalizer of the VSB reception system uses thesequence to enhance ghost cancellation performance of both thesupplemental data and the MPEG data and the Trellis decoder uses thesequence to improve noise performance of supplemental data. As shown inFIG. 4, upon reception of one supplemental data byte, the null sequenceinserter 22 for generating the predefined sequence inserts null bits, toprovide two bytes.

The inserted null sequence is processed in the VSB transmission system25 in FIG. 3, and then transmitted to the VSB reception system. The nullsequence is randomized by the data randomizer 1 of the VSB transmissionsystem 25, and coded by the Reed-Solomon coder 2. Then, the nullsequence is interleaved by the data interleaver 3, and provide to theTrellis coder 4 as an input signal D0. This converted sequence is thepredefined sequence. The input signal D0 is a lower bit of the two inputbits to the Trellis coder 4. The Trellis coder is basically operativesuch that three bits are provided with two received bits.

The VSB reception system generates the sequence received as the inputsignal D0 from the Trellis coder in the 8T-VSB transmission system 25,i.e., the predefined sequence, and uses the generated sequence forimproving the performance of the VSB reception system. Alternatively,other sequences known to one of ordinary skill in the art may be usedinstead of the null sequence described above.

The VSB transmitter 95 of the present invention is required to havesubstantially identical probabilities of occurrence of the 8 levels, forhaving backward-compatibility with the related art VSB transmissionsystem. Therefore, the presence of the 0's and 1's in the sequencereceived as the input signal D0 at the Trellis coder are required to bealmost the same.

FIG. 5 illustrates a block diagram of the components of the trelliscoder 4 used in the VSB transmission system 25 in FIG. 3. FIG. 6illustrates state transition diagrams of the Trellis coder shown in FIG.5. The trellis coder 4 comprises a coder 28, a precoder 27 and amodulator 29.

In FIG. 5, the Trellis coder 28 and the precoder 27 receive two inputbits D0 and D1 and provide three output bits C0, C1, and C2. An 8T-VSBmodulator 29 provides modulated values ‘z’ of the three output bits C0,C1, and C2. In FIG. 5, reference numerals 27 a and 28 b denote adders,and 27 b, 28 b, and 28 c denote registers.

As shown in FIG. 5, the input bit D1 is precoded into the output bit C2by the precoder 27. The input bit D0 is the same as the output bit C1.The output bit C0 is a value stored in the register 28 c of the Trelliscoder 28. Signal levels are determined by an output bitstream C0, C1,and C2 of the Trellis coder 28 and the precoder 27, wherein there are 8whole signal levels (−7, −5, −3, −1, +1, +3, +5, +7). The whole signallevels are divided into two groups of signal levels (−7, −3, +1, +5)(−5, −1, +3, +7) each with 4 levels according to the output bit C0. Inother words, one out of the two groups of signal levels (−7, −3, +1, +5)(−5, −1, +3, +7) each with 4 levels are selected according to the valuestored in register 28 c.

Therefore, if the estimation of the present value stored in the register28 c in the coder 28 is possible, prediction of an output signal levelof the coder 28 falling on one of the two signal level groups ispossible. In other words, to estimate the present value of the register28 c in coder 28 means to predict one of the two signal level group inwhich the next output signal of the coder 28 will fall on. As a result,a four level slicer having two times the distance between each signallevel can be used instead of a conventional 8 level slicer with reducedsignal level separations.

In order to estimate the value stored in the register 28 c of the coder28, the Viterbi algorithm is preferably used for the Trellis decoder 52of the VSB reception system 100 (shown in FIG. 8). If a wrong predictionis made on the signal level groups, the prediction error can be higher.Therefore, for minimizing the prediction error, the conventional 8T-VSBreception system 150 (shown in FIG. 2) uses the four level slicer if theprediction reliability is high, and/or uses an original 8 slicer if theprediction reliability is low.

The present invention improves the prediction reliability significantlyby using the predefined sequence transmitted from the VSB transmissionsystem. Preferably, both the slicer predictor and the Trellis decoderused in the VSB reception system use the Viterbi algorithm.

The Viterbi algorithm estimates one of state transitions (or paths) thathas the highest probability with respect to time. As expressed inequation (1), the probability that a state value of the Trellis coder 28is ‘Si’ at a time ‘k’ is proportional to a cumulative metric Mi of thestate value SiP(Si)∝e^(−Mi)  (1)

A cumulative metric up to the time ‘k’ can be expressed as equation (2),where ‘yj’ denotes a received 8T-VSB signal value, and ‘xj’ denotes alevel value of the 8T-VSB signal assigned to a branch connecting betweenstates in the state transition drawing of FIG. 6.

$\begin{matrix}{{Mi} = {\sum\limits_{j = 1}^{k}\left( {{yj} - {xj}} \right)^{2}}} & (2)\end{matrix}$

As shown in the state transition diagram of FIG. 6, since the input bitto the Trellis coder 28 has two bits, the number of branches connectingthe states is four. Of the four paths connecting respective states S1,S2, S3, and S4, the Viterbi algorithm selects and stores a path havingthe least cumulative metric value. A part that carries out such aprocess is called an ACS (Accumulate/Compare/Select) module. Byselecting a metric having the smallest value from the metrics selectedand stored in the respective states S1, S2, S3, and S4, a state of thehighest probability at the time ‘k’ can be selected.

In the VSB transmitter 95 for digital TV broadcasting shown in FIG. 3,the null sequence is inserted in the supplemental data, and thepredefined sequence is transmitted to the VSB reception system throughthe bit D0 received at the Trellis coder. Preferably, the use of thepredefined sequence at the VSB reception system may significantlyimprove performance of the Viterbi algorithm.

For example, the case when the bit of the predefined sequencetransmitted from the transmission system at the time ‘k’ is ‘1’ will bediscussed. In this case, it is impossible that the branches having D1and D0 being 00 and 10 among the four branches connecting the states S1,S2, S3, and S4 are selected to be the path of the highest probability.

The case when a bit D1 of the predefined sequence is ‘0’ will bediscussed. In this case, it is impossible that the branches having D1and D0 being 01 and 11 among the four branches connecting the states S1,S2, S3, and S4 are selected to be the path of the highest probability.At the end, the use of the predefined sequence permits the ACS module toreduce the number of branches from four to two by using the Viterbialgorithm. As a result, the performance of the Trellis decoder and thereliability of the slider predictor in the reception system issignificantly improved.

In the ATSC 8T-VSB reception system 150 in FIG. 2, the channel equalizer13 and the phase tracker 15 use a slicer and a slicer predictor 14,respectively. In general, the slicer predictor 14 in the phase trackeris included in the Trellis decoder 16.

FIG. 7 illustrates a diagram of an ATSC 8T-VSB Trellis coder 4 includedin the VSB transmission system 25 in FIG. 3. The VSB Trellis coder 4includes, for example, the 12 Trellis coder and precoders 32-1 to 32-12,a multiplexer 30 having output terminals connected to input terminals ofthe Trellis coder and precoders 32-1 and 32-12, and a multiplexer 31having an output terminals connected to output terminals of the Trelliscoder and precoders 32-1 to 32-12.

FIG. 8 illustrates a block diagram of a digital VSB reception system 300in accordance with a preferred embodiment of the present invention,which improves reception performance by using a predefined sequence andreceives supplemental data transmitted by the VSB transmitter.

In FIG. 8, the VSB reception system 300 of the present inventionincludes a sequence generator 46 for indicating a symbol of thesupplemental data and generating a predefined sequence include din thesupplemental data and generating a predefined sequence included in thesupplemental data, a modified legacy VSB receiver 100 for processing thedata received from the VSB transmitter 95 (shown in FIG. 3) in a reverseorder of the VSB transmission system. The VSB reception system 300further includes a demultiplexer 56 for demultiplexing the data from themodified legacy VSB receiver 100 into the MPEG data (also known as datasegment) and the supplemental data (also known as data segment), and asupplemental data processor 200 for processing the supplemental datasegment from the demultiplexer 56 in reverse order of the transmissionsystem, to obtain the original supplemental data.

As shown in FIG. 8, the modified legacy VSB receiver 100 includes ademodulator 47, a comb filter 48, a channel equalizer 49, a slicerpredictor 50, a phase tracker 51, a Trellis decoder 52, a first datadeinterleaver 53, a first Reed-Solomon decoder 54, and a datade-randomizer 55. The supplemental data processor 200 includes an MPEGheader remover 56, a null sequence remover 58, a second data interleaver59, and a second Reed-Solomon decoder 60.

According to the preferred embodiment, the demodulator 47 converts a RFband signal into a base band signal, and the synchronizing and timingrecovery system (not shown) recovers a segment synchronizing signal, afield synchronizing signal, and a symbol timing. The comb filter 48removes an NTSC interference signal, if detected, and the channelequalizer 49 corrects a distorted channel by using the slicer predictor50.

The phase tracker 51 corrects a rotated phase, and the Trellis decoder52 undertakes Viterbi decoding by using the generated sequence and theViterbi algorithm. The channel equalizer 49, the slicer predictor 50,the phase tracker 51, and the Trellis decoder 52 process the receivedsymbols by using the sequence generated at the sequence generator 46.

The first data deinterleaver 53 acts in reverse of the action of thedata interleaver in the ATSC 8T VSB transmission system, and the firstReed-Solomon decoder 54 again decodes a signal Reed-Solomon coded at theATSC 8T VSB transmission system. The data derandomizer 55 acts inreverse of the action of the data randomizer in the transmission system.

According to the preferred embodiment of the present invention thesequence generator 46 indicates if the received symbol is the supplementdata symbol or not, and generates a sequence identical to the predefinedsequence that is inserted and transmitted in the supplemental data.

The slicer predictor 50 is the ACS part of the trellis decoder. In otherwords, the slicer predictor 50 is a trellis decoder with decoding depth0. The slicer predictor 50 estimates the state transition sequence.After the ACS operation, the slicer predictor 50 estimates the maximumlikely sequence and predicts one of the signal level groups on which thenext symbol might fall.

As described above, the channel equalizer 49, the slicer predictor 50,the phase tracker 51, and the Trellis decoder 52 improve signalprocessing performances by using the predefined sequence. This occurswhen the components using the predefined sequence use the sequenceinformation with the delayed sequence information, taking the delay indata processing at prior components into account.

In the VSB reception system 300, the demultiplexer 56 demultiplexes thedata from the modified legacy VSB receiver 100 into a supplemental datasegment and an MPEG data segment by using the multiplexing informationdetected from, for example, the field synchronizing signal. In thepreferred embodiment the first Reed-Solomon decoder 54 makes noReed-Solomon decoding of the supplemental data segment, but only removesthe 20 byte parity bits added at the Reed-Solomon coder in the VSBtransmission system.

If the channel noise is excessive, many errors are present in the paritybytes of the Reed-Solomon code compared to the supplemental data becausethe parity bytes of the ATSC Reed-Solomon code has no predefinedsequence inserted, resulting in no gain at the Trellis decoder 52. Thefirst Reed-Solomon decoder 54 makes no Reed-Solomon decoding of thesupplemental data segment because it is highly possible that the firstReed-Solomon decoder 54 makes an erroneous correction in the case wherethe supplemental data segment has an error in excess of, for example, 10bytes.

The supplemental data segment from the demultiplexer 56 is provided tothe MPEG header remover 57. The MPEG header remover 57 removes 3 bytesof MPEG header from the supplemental data segment. The MPEG header isinserted when the supplemental data is transmitted in an ATSC format atthe VSB transmission system.

The null sequence remover 58 then removes the null sequence inserted inthe supplemental data segment at the null sequence inserter in the VSBtransmission system. The second data deinterleaver 59 acts in reverse ofthe interleaving process on the supplemental data segment in the VSBtransmission system. If the interleaving process is omitted in the VSBtransmission system, the VSB reception system 300 may disable the seconddeinterleaver 59 or not include it at all. The second Reed-Solomondecoder 60 decodes the Reed-Solomon code of the supplemental datasegment.

The phase tracker 15 of the related art ATSC 8T-VSB reception system(shown in FIG. 2) also selectively uses the slicers therein in responseto the slicer predictor. The phase tracker 51 of the VSB receptionsystem 300 of the present invention is different from the related artVSB reception system in that the predefined sequence is used in theprediction and selection of the slicer. The phase tracker uses slicersto correct the phase error, so it also uses the slicer with the aid ofslicer prediction from trellis decoder. The selective use of slicer ofthe phase tracker is the same with that of the equalizer.

Since the predefined sequence is inserted in the supplemental datasymbol only, the VSB reception system 300 is required to identify thesupplemental data symbol, and to determine whether the predefinedsequence from the transmission system is ‘0’ or ‘0’.

There are two methods for identifying information on the supplementaldata symbol and the predefined sequence at the VSB reception system 300.In the first method, symbols of one field of one ATSC data frame arestored in advance in ROM (Read Only Memory). Since the data derandomizerof the ATSC 8T-VSB transmission system is initially synchronized to thefield synchronizing signal, the cycles of the predefined sequence isalso in field units. However, the first method requires a large memorybecause the predefined sequence is required to be stored in field unitsaccording to a multiplexing method in the transmission system. In thesecond method, the VSB reception system has a transmitter for generatingthe predefined sequence as its own.

FIG. 9 illustrates a block diagram of the sequence generator 46 in thereception system of the present invention according to the secondmethod. The sequence generator 46 includes a multiplexer 61, a modifiedrandomizer 62, a dummy parity inserter 63, a data interleaver 64, and aTrellis coder 65. The multiplexer 61 has a supplemental data dummypacket and an MPEG data dummy packet provided thereto. The MPEG datadummy packet produces 187 dummy bytes of 0x00. The supplemental datadummy packet produces three dummy bytes of 0x00 for the MPEG headerbytes, and 184 dummy bytes of 0xAA for the supplemental data. Thosedummy bytes are multiplexed at the multiplexer 61 and randomized at themodified randomizer 62.

The modified randomizer 62 randomizes the output of the multiplexer 61by subjecting the intentionally produced pseudo random bytes and 0x55,for example, to bit-wise AND operation, and a resultant of the ANDlogical operation and input bits from the multiplexer 61 to bit-wiseexclusive OR operation. Then, the dummy parity inserter 63 inserts thedummy bytes 0x00 of the 20 parities added by the Reed-Solomon coder ofthe ATSC 8T-VSB transmission system to the randomized data. The outputof the dummy parity inserter 63 is interleaved at the data interleaver64. The trellis coder 65 converts the interleaved dummy bytes intosymbols and each byte produces four symbols. A detail of the Trelliscoder 65 is shown in FIG. 7.

The symbols are provided to the 12 Trellis coder and precoders 32-1 to32-12. The symbols are preferably not subjected to precoding and Trelliscoding, but forwarded as provided. Each of the symbols finally forwardedthus has two bits D1 D0. In this instance, if the bit D1 is ‘1’, thesymbol is the supplemental data symbol, and if the bit d1 is ‘0’, thebit D0 is the MPEG data symbol. If the bit D1 is ‘1’, the bit D0 is thepredefined sequence that is provided to the Trellis coder of thetransmission system. The sequence generator 46 is operative synchronousto the field synchronizing signal recovered at the reception system.

FIG. 10A illustrates signal level diagrams of three kinds of slicersused for MPEG data symbols used in the channel equalizer 49. Each slicershows signal levels. Each slicer determines a signal that has theshortest distance to a signal received from the transmission system. Ifthe prediction reliability of the slicer prediction is low, the slicer 1having 8 levels is used. If the prediction reliability of the slicer ishigh, either the slicer 2 or the slicer 3 is selected according to aestimation of the register 28 c in the coder 28 shown in FIG. 5. If avalue the register 28 c estimated is ‘0’, the slicer 2 is selected andthe estimated value is ‘1’, the slicer 3 is selected.

FIG. 10B illustrates signal level diagrams of six kinds of slicers usedfor supplemental data symbols. If the symbols are symbols of thesupplemental data, the six slicers can be used by using the bit D1 ofthe predefined sequence. When the sequence bit D0 is ‘0’, a signal levelgroup transmitted from the VSB transmission system is (−7, −5, +1, +3).When the sequence bit D0 is ‘1’, a signal level group transmitted fromthe VSB transmission system is (−3, −1, +5, +7). When the reliability ofthe slicer predictor is poor, either the slicer 4 or the slicer 5 isselected, depending on the value of the sequence bit D0.

A case when the slicer predictor has a high reliability will bediscussed. When the sequence bit D0 is ‘0’, the slicer 4 may be dividedinto two slicers of 6 and 7, according to a value stored in the register28 c of the Trellis coder 28. If the value stored in the register 28 cis ‘0’, the slicer 6 is selected, and if value stored is ‘1’, the slicer7 is selected.

If the sequence bit D0 is ‘1’, the slicer 5 is divided into two slicersof slicer 8 and slicer 9, according to a value stored in the register 28c of the Trellis coder 28. Therefore, if the value stored in theregister 28 c is ‘0’, the slicer 8 is selected, and if the value storedin the register 28 c is ‘1’, the slicer 9 is selected.

As discussed, the slicers 6, 7, 8, 9 in FIG. 10B may be compared to therelated art slicers 2, 3 in FIG. 10A to find that a signal distance ofthe slicers 6, 7, 8, 9 is greater by two times than the related artslicers 2, 3. Therefore, in the case of the supplemental data symbol,slicers each having a greater slicer distance can be used with the useof a predefined sequence, resulting in a consequential reduction ofdecision error.

FIG. 11 illustrates a block diagram of a channel equalizer 49 of the VSBreception system 300 of the present invention using the predefinedsequence. In FIG. 11, the channel equalizer includes a feed-forwardfilter 66, a feedback filter 67, an adder 68 for adding outputs of thefilters 66 and 67, nine slicers 69-1 to 69-9, a multiplexer 70, and acontroller 71.

According to the preferred embodiment, an input signal to the channelequalizer 49 is provided to the feed-forward filter 66, and an outputsignal of the feed-forward filter 66 and an output signal of thefeedback filter 67 are added at the adder 68. An output signal of theadder 68 is an output signal of the channel equalizer 49. The outputsignal of the channel equalizer 68 is provided to the nine slicers 69-1to 69-9 in common, for the slicers 69-1 to 69-9 to decide the signallevel.

The controller 71 controls the multiplexer 690 such that the multiplexer70 selects one of the outputs of the slicers 69-1 to 69-9 and providesto the feedback filter 67, and the controller 71. The controller 71updates filter coefficients of the feed-forward filter 66 and thefeedback filter 67 by using the selected slicer output and the output ofthe channel equalizer 49. As shown in FIG. 8, the slicer predictor 50receives the output signal of the channel equalizer 49 and the outputsignal of the sequence generator 46, and predicts a value stored in theregister 28 c of the Trellis coder 28 in the VSB transmission system byusing the received signals. The slicer predictor 50 then calculates thereliability of the predicted value, and forwards the values to thecontroller 71 of the channel equalizer 49.

The controller 71 of the channel equalizer 49 receives information onthe symbol received as being the supplemental data or the MPEG data, andthe predefined sequence D0 inserted in the supplemental data symbol fromthe sequence generator 46. The controller 71 receives the estimatedvalue of the register 28 c of the Trellis coder 28 in the transmissionsystem together with the prediction reliability from the slicerpredictor 50, and, selects one of the outputs of the nine slicers 69-1to 69-9.

As described above, the VSB reception system 300 according to thepreferred embodiment of the present invention has the followingadvantages. First, the VSB reception system has components forprocessing both the MPEG data and the supplemental data.

Second, the sequence generator 46 provided in the VSB reception system300 (for generating a predefined sequence as an input signal to aTrellis coder of a transmission system) can improve receptionperformance of the reception system with respect to a channel ghostsignal and a noise signal over the related art ATSC 8T-VSB receptionsystem. Particularly, performances of the slicer predictor and theTrellis coder in the reception system are significantly improved.

Third, by using the predefined sequence, the VSB reception system 300can use slicers each having a greater signal distance than theconventional slicers at the channel equalizer and the phase trackertherein, which minimizes decision error. This enhances the trackerdeghosting performance of the equalizer and the phase trackingperformance of the phase tracker.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the VSB communicationsystem, and the signal format for the VSB communication system of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

1. A digital television receiver, comprising: a demodulator adapted todemodulate an input signal containing first service data multiplexedwith second service data; a first forward error correction (FEC) decoderadapted to decode the demodulated signal for first forward errorcorrection (FEC) and remove first parity data from the FEC-decoded firstand second service data in order to correct errors in the first andsecond service data that occurred during reception of the input signal;a demultiplexer adapted to demultiplex the first service data and thesecond service data from the FEC-decoded signal; and a second forwarderror correction (FEC) decoder adapted to decode the demultiplexed firstservice data for second forward error correction (FEC) and remove secondparity data from the FEC-decoded first service data in order toadditionally correct errors in the first service data that occurredduring the reception of the input signal, wherein a length of the firstparity data is different from a length of the second parity data.
 2. Thedigital television receiver of claim 1, wherein the first FEC decodercomprises a first Reed-Solomon (RS) decoder.
 3. The digital televisionreceiver of claim 2, wherein the second FEC decoder comprises a secondReed-Solomon (RS) decoder.
 4. The digital television receiver of claim1, wherein the length of the first parity data is less than the lengthof the second parity data.
 5. The digital television receiver of claim1, further comprising an MPEG header remover adapted to remove MPEGheaders from the demultiplexed first service data.
 6. The digitaltelevision receiver of claim 1, further comprising a data deinterleaveradapted to deinterleave the first and second service data in thedemodulated signal.
 7. The digital television receiver of claim 1,further comprising a channel-equalizer adapted to channel-equalize thedemodulated signal.
 8. The digital television receiver of claim 1,further comprising a trellis decoder adapted to decode the demodulatedsignal using a Viterbi decoding algorithm.
 9. The digital televisionreceiver of claim 1, wherein the demodulator is further adapted todetect sync information in the input signal.
 10. A method of decoding adigital broadcast signal, the method comprising: demodulating an inputsignal containing first service data multiplexed with second servicedata; decoding the demodulated signal for first forward error correction(FEC) and removing first parity data included in the FEC-decoded firstand second service data in order to correct errors in the first andsecond service data that occurred during reception of the input signal;demultiplexing the first service data and the second service data fromthe FEC-decoded signal; and decoding the demultiplexed first servicedata for second forward error correction (FEC) and removing secondparity data included in the FEC-decoded first service data in order toadditionally correct errors in the first service data that occurredduring the reception of the input signal, wherein a length of the firstparity data is different from a length of the second parity data. 11.The method of claim 10, wherein decoding the demodulated signal forfirst FEC comprises Reed-Solomon (RS) decoding the first and secondservice data included in the demodulated signal.
 12. The method of claim11, wherein decoding the demultiplexed first service data for second FECcomprises Reed-Solomon (RS) decoding the demultiplexed first servicedata.
 13. The method of claim 10, wherein the length of the first paritydata is less than the length of the second parity data.
 14. The methodof claim 10, further comprising removing MPEG headers from thedemultiplexed first service data.
 15. The method of claim 10, furthercomprising deinterleaving the first and second service data in thedemodulated signal.
 16. The method of claim 10, further comprisingchannel-equalizing the demodulated signal.
 17. The method of claim 10,further comprising detecting sync information in the input signal.
 18. Abroadcast transmitter, comprising: a first forward error correction(FEC) coder adapted to code first service data for first forward errorcorrection (FEC) by adding first parity data in order to reduce errorsin the first service data that occur during data transmission; amultiplexer adapted to multiplex the FEC-coded first service data andsecond service data; a second forward error correction (FEC) coderadapted to code the multiplexed first and second service data for secondforward error correction (FEC) by adding second parity data in order toreduce errors in the first and second service data that occur duringdata transmission, wherein a length of the first parity data isdifferent from a length of the second parity data; and a modulatoradapted to modulate the FEC-coded first and second service data for datatransmission.
 19. The broadcast transmitter of claim 18, wherein thefirst FEC coder comprises a first Reed-Solomon (RS) coder.
 20. Thebroadcast transmitter of claim 19, wherein the second FEC codercomprises a second Reed-Solomon (RS) coder.
 21. The broadcasttransmitter of claim 18, wherein the length of the first parity data isgreater than the length of the second parity data.
 22. The broadcasttransmitter of claim 18, further comprising an MPEG header inserteradapted to insert MPEG headers in the FEC-coded first service data. 23.The broadcast transmitter of claim 18, further comprising a datainterleaver adapted to interleave the FEC-coded first and second servicedata.
 24. The broadcast transmitter of claim 18, further comprising atrellis coder adapted to trellis-code the FEC-coded first and secondservice data.
 25. The broadcast transmitter of claim 18, furthercomprising a mapper adapted to map the FEC-coded first and secondservice data into corresponding symbols.
 26. The broadcast transmitterof claim 18, further comprising a frame formatter adapted to add syncinformation to the FEC-coded first and second service data.
 27. A methodof encoding a digital broadcast signal, the method comprising: codingfirst service data for first forward error correction (FEC) by addingfirst parity data in order to reduce errors in the first service datathat occur during data transmission; multiplexing the FEC-coded firstservice data and second service data; coding the multiplexed first andsecond service data for second forward error correction (FEC) by addingsecond parity data in order to reduce errors in the first and secondservice data that occur during data transmission, wherein a length ofthe first parity data is different from a length of the second paritydata; and modulating the FEC-coded first and second service data fordata transmission.
 28. The method of claim 27, wherein coding firstservice data for first FEC comprises Reed-Solomon (RS) coding the firstservice data.
 29. The method of claim 28, wherein coding the multiplexedfirst and second service data comprises Reed-Solomon (RS) coding themultiplexed first and second service data.
 30. The method of claim 27,wherein the length of the first parity data is greater than the lengthof the second parity data.
 31. The method of claim 27, furthercomprising inserting MPEG headers in the FEC-coded first service data.32. The method of claim 27, further comprising interleaving theFEC-coded first and second service data.
 33. The method of claim 27,further comprising trellis-coding the FEC-coded first and second servicedata.
 34. The method of claim 27, further comprising mapping theFEC-coded first and second service data into corresponding symbols. 35.The method of claim 27, further comprising adding sync information tothe FEC-coded first and second service data.
 36. A digital television(DTV) receiver, comprising: a demodulator configured to demodulate adigital television (DTV) signal containing first service datamultiplexed with second service data; a first decoder configured todecode the demodulated DTV signal for first error correction in order tocorrect errors in the first and second service data that occurred duringreception of the DTV signal; a data extractor configured to extract thefirst service data from the decoded DTV signal; and a second decoderconfigured to decode the extracted first service data for second errorcorrection in order to additionally correct errors in the first servicedata that occurred during the reception of the DTV signal.
 37. The DTVreceiver of claim 36, wherein the first decoder comprises a trellisdecoder configured to perform trellis decoding on the first and secondservice data in the demodulated DTV signal.
 38. The DTV receiver ofclaim 37, wherein the second decoder comprises a second Reed-Solomon(RS) decoder configured to remove parity data from the extracted firstservice data.
 39. A method of processing digital broadcast data, themethod comprising: demodulating a digital television (DTV) signalcontaining first service data multiplexed with second service data;decoding the demodulated DTV signal for first error correction in orderto correct errors in the first and second service data that occurredduring reception of the DTV signal from a broadcast transmitter;extracting the first service data from the decoded DTV signal; anddecoding the extracted first service data for second error correction inorder to additionally correct errors in the first service data thatoccurred during the reception of the DTV signal.
 40. The method of claim39, wherein decoding the demodulated DTV signal for first errorcorrection comprises performing trellis decoding on the first and secondservice data in the demodulated DTV signal.
 41. The method of claim 39,wherein decoding the extracted first service data for second errorcorrection comprises performing Reed-Solomon (RS) decoding on theextracted first service data.